This invention relates generally to a device for securing a tool to a fixture and specifically to a retainer which engages a recess within a punch or die assembly.
Within the equipment, tool and die making industries, it is common to provide various fastening means between machinery components. For example, sheet metal stamping and injection molding dies are typically fastened to their respective die plates by bolts extending through countersunk holes within the die. These bolts have a head which engages the die and a threaded shank which enmeshes with a receiving hole in the die plate. Typically four or more bolts are required to retain each die.
Other conventional die holding devices are known which employ a plurality of gooseneck clamps, dog clamps, wedge bevels or the like. Examples of such devices are disclosed within U.S. Pat. No. 4,912,961 entitled "Structure for Securing a Die to a Bolster Plate" which issued to Brown on Apr. 3, 1990, U.S. Pat. No. 3,269,168 entitled "Die Apparatus" which issued to Anderson on Aug. 30, 1966, U.S. Pat. No. 2,028,354 entitled "Adjustable Die Holder" which issued to Roe on Jan. 21, 1936, U.S. Pat. No. 1,778,339 entitled "Die Holder" which issued to Rafter on Oct. 14, 1930, Japanese Patent Publication No. 56-50732 entitled "Upper Die Clamping Device in Forging Press" to Sumitomo Jukikai Kogyo K.K. (May 8, 1981), Japanese Patent Publication No. 4-158944 entitled "Die Clamping Mechanism for Punching Press" to Murata Mach Ltd. (Jun. 2, 1992), Soviet Union Patent No. 161209 entitled "Device for Securing Hammer Blocks on Radial-Forging Machines" to Reznikov (Apr. 9, 1964,) and D. Eary and E. Reed, Techniques of Press Working Sheet Metal: An Engineering Approach to Die Design, Second Edition, Prentice-Hall, Inc. (1974) at pages 323-333. However, all of these conventional devices require multiple fasteners for each tool, are not well suited for engagement with cylindrically-shaped tools, appear to be too inaccurate for use with small tools (e.g., having an outer diameter of approximately 10 mm) and are prone to loosening in the highly vibration prone work environment thereby leading to inaccurate tool placement, premature tool failure and poor quality processed parts.
In accordance with the present invention, the preferred embodiment of a device for securing a tool includes a punch or die having a recess disposed within an exterior surface for mating with an engagement member. Another aspect of the present invention provides an engagement member with a partially spherical external surface and an internal passageway for receiving a threaded shank of a screw. In a further aspect of the present invention, the recess has an undercut section, a generally flat middle section and a partially spherical section, wherein the partially spherical external surface of the engagement member mates with the partially spherical section of the tool recess. In yet another aspect of the present invention, the tool is a sheet metal joining punch. In still another aspect of the present invention, the tool is a sheet metal joining die. A method of securing a tool to a fixture is also provided.
The present invention is advantageous over traditional devices in that the present invention secures a tool to a fixture by use of a single retainer. This leads to extremely quick tool changeover which promotes higher productivity and lower set up costs. The shape of the recess and engagement member have also proven extremely advantageous over conventional devices since they cause a highly secure wedging action upon affixation or enmeshing so as to accurately and repeatedly locate and maintain the tool in the desired position. This reduces premature failure and breakage of mating punches and dies while also improving processed part-to-part tolerances and repeatability throughout prolonged usage in the typically harsh plant environment. The directional forces caused by the engaged interaction of the fixture, tool and retainer also promote accurate and secure retention. Additional advantages and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.